This invention relates to sand consolidation of subsurface formations surrounding a wellbore penetrating a hydrocarbon-bearing reservoir and, more particularly, to a method of carrying out in-situ combustion within such formation to effect such consolidation.
In order to limit sand production from hydrocarbon-bearing reservoirs within unconsolidated or loosely consolidated sandstone formations with high clay content, various methods have been employed for preventing sands from entering the production stream. One conventional technique involves the provision of a gravel pack around the wellbore which acts as a filter and prevents production of formation sand. Such a gravel pack generally comprises a region of packed sand and a screen or perforated conduit which is used to aid in communicating fluids through the gravel or sand pack to unpacked regions of the wellbore. Although such gravel packs are often successful at reducing sand production from unconsolidated pay zones, such gravel packs are often difficult to complete and may substantially increase the cost of well production. Also, difficulties often are encountered in removing the gravel pack when it is desired to recomplete or otherwise work over the well.
Another technique involves the injection of resins (i.e., certain epoxies, phenolics and furans) into the formation to effect consolidation. These materials are expensive and work with varying degrees of success. Formation permeability is difficult to control since the resin fills the pore spaces. Resin is difficult to pump and place effectively in the formation. Only limited intervals of about 10 feet or less can be treated effectively. Gravity effects in deviated wellbores cause a problem with placement efficiency because resins are typically pumped as a thin fluid which must be contacted with a catalyst which is pumped in the latter part of the treatment.
Various techniques have been used for heating in-situ such formations. One such technique involves the injection of a heated fluid through the wellbore into the surrounding formation. Another involves the use of downhole heating devices such as electric or gas heaters. One serious shortcoming of such heating techniques is that they often result in uneven heating of the formation. For example, in the injection of a hot fluid into the formation, the fluid will preferentially flow into zones of the formation having relatively high permeability. This results in the occurrence of so-called "hot spots" at the face of the formation where high permeability zones exist with the attendant occurrence of "cold spots" between these zones.